1. Field of the Invention
The present invention relates to a method of fabricating an element having a microstructure.
2. Description of the Related Art
Elements having microstructures are known as micro-electronic devices. Japanese Examined Patent Publication (Kokoku) No. 7-114289 discloses an example of the micro-electronic device. An example of the element having a microstructure is an MEMS device that is applied to ultra-small optical switches, acceleration sensors, gyro-sensors, and so forth. The MEMS device comprises a substrate and a movable microstructure provided on the surface of the substrate (sheet-like member). Another example of the element having a microstructure is an element used in the radio frequency (RF) range. In the element used in the radio frequency (RF) range, a micro aerial wiring called “air bridge” is applied to the surface of the substrate (sheet-like member).
In the construction of the element having a microstructure, an electric circuit, etc, is formed in the sheet-like member, a microstructure is formed on the surface of the sheet-like member, and the sheet-like member is divided into a plurality of elements (chips) by a dicing operation using an abrasive blade. In the dicing, the sheet-like member is held by a vacuum chuck, or held by a vacuum chuck while it is fixed to an adhesive sheet, and is diced with the abrasive blade.
Dicing by use of the abrasive blade involves the problem that the element is likely to be damaged by mechanical vibration or impact. In the element having a microstructure, in particular, the microstructure formed on the surface of the substrate is likely to be damaged by vibration and impact.
The inventors of the present application have realized, specifically, conducting dicing while the microstructure formed on the surface of the substrate is protected or reinforced during production of the element having a microstructure.
Japanese Unexamined Patent Publication (Kokai) No. 59-17264, No. 2001-345533, No. 1-188308, and No. 10-230429 disclose a dicing method in which a semiconductor wafer is held by a vacuum chuck by using a refrigerated matter. The refrigerated matter is arranged in a tray-like holder having a cavity. The tray-like holder is fitted to the vacuum chuck. The semiconductor wafer is inserted into the cavity during use and a liquid such as water or silicone oil is charged. The liquid flows between the semiconductor wafer and the bottom surface of the cavity and is solidified when it is cooled (refrigerated). The semiconductor wafer is fixed to the vacuum chuck by the refrigerated matter so solidified and by the holder.
In this method, processing can be carried out safely, reliably and highly precisely without using an adhesive sheet. When the liquid such as water or silicone oil is applied to the surface of the semiconductor wafer, the liquid is solidified between the semiconductor wafer and the bottom surface of the cavity of the holder and also on the surface of the semiconductor wafer. Consequently, dicing can be carried out while the surface of the semiconductor wafer is covered with the refrigerated matter.
In this method, cooling is stopped after completion of dicing and the refrigerated matter is melted into the liquid. Therefore, individual elements can be removed from the holder. However, the individual elements are not held together and are separated one by one, so a problem develops when the individual elements are transferred to a subsequent process step. For example, it is difficult to automatically set the freely separated elements to a conveyor device and when the element is mounted to a substrate, an automatic mounting apparatus cannot be used.